I did a whole transmission twice in a vapor honing setup. It took forever! Looks amazing though.  

What was the cost?  How do they charge for their service?

4 hours ago, inline6 said:

What was the cost?  How do they charge for their service?

Those 4 pieces were $150 total.  I thought the price was so good that I brought a second set for the same treatment. This new set is dirtier, so it may cost a little more to de-grease.

For the 1971 Monte Carlo, the Works team appeared to employ (from what information I can gather) what is basically a 2-channel power amp with gain control to facilitate communication between driver and navigator.  The essentially muffler-less cars were already loud to begin with (by all accounts), and subtracting any sound deadening, plus the incessant constant rattling of two in-cabin fuel pumps, one could imagine the occupants would be losing their voices around day 2.  Interestingly, I have a fair number of period photos where the team did not appear to be wearing headsets while underway, so perhaps the system didn't provide the expected benefit, apart from when the occupants donned helmets.

I believe mine to be original hardware, as I have a detailed picture of it installed in the car from the 71 Monte Carlo (last picture below), and another from October 1971. It is a very compact 12V device, made by Teikoku Dempa Co. LTD, using 1/4" headphone jacks to a pair of mono headsets with microphones. Teikoku Dempa has been in business since the 1940s, making radios under the Clarion brand name. It's not clear to me whether this device was stock, a special order by the Works team, or potentially even a modified over-the-counter item. The unit wasn't working, so I decided to take it apart for a little exploration and diagnosis.   It didn't take long to discover a fair number of leaky capacitors, which are in need of replacement.  Probably best to replace all that I can find components for. 

Although Ive taken a circuits class in my youth, I'm not an electronics repairman, so I'm on the hunt for an enterprising repair shop, likely a tinkerer with an oscilloscope who would want to spend a few hours reverse engineering the board, replacing the caps, and matching the system to my headsets.  I'm taking a first-pass stab at creating a circuit diagram using some simple circuit design tools, so whomever takes on the job isn't starting from scratch.

Worst case scenario is that I'm forced to put the original electronics aside for storage, and retrofit the box with a modern 2-channel amp, so it at least looks the same. In the mean time, it would be fun to find out where the Clarion on/off switch and volume knob came from.  Perhaps there is an old Clarion transistor radio which uses the same equipment?

Edited March 23, 20232 yr by xs10shl

That board is mostly symmetric about the middle. Undoubtedly the two independent channels. It'll save you quite a bit of time with the reverse engineering because you only have to do half.

This is what I mean:

I would guess that the few components at the bottom of the pic that are not symmetric (the coil and the big cap) are most likely input power filtering, and the big cap at the top is most likely a power supply filter as well. The big ring of solder trace around the board perimeter is ground and the big strip running down the middle is most likely the high side of the supply.

10 hours ago, xs10shl said:

For the 1971 Monte Carlo, the Works team appeared to employ (from what information I can gather) what is basically a 2-channel power amp with gain control to facilitate communication between driver and navigator.  The essentially muffler-less cars were already loud to begin with (by all accounts), and subtracting any sound deadening, plus the incessant constant rattling of two in-cabin fuel pumps, one could imagine the occupants would be losing their voices around day 2.  Interestingly, I have a fair number of period photos where the team did not appear to be wearing headsets while underway, so perhaps the system didn't provide the expected benefit, apart from when the occupants donned helmets.

Nissan's Works team called this system an 'Interphone' (the period English vernacular being 'Intercom') and they had already been using similar systems on previous Works rally cars. They were especially important/useful on the East African Safari Rally with its long and arduous road sections between special stages, where it was still necessary for the navigator to call the route to the driver, often at fairly high speeds (high noise). They would have been necessary on 'recce'/reconnaisance practice and ice note runs where the crew needed good communication to make accurate pace notes on events such as the Monte and RAC rallies. 

For the 1970 RAC Rally, the crews were using single-ear interphones that could be used also be used over specially-adapted Paddy Hopkirk crash helmets. Kind of unwieldy, and it is easy to see why the next step was to integrate the earphone on the inside of the helmet.

Some photos of testing in the UK prior to the 1970 RAC Rally, where the crews were getting used to the new systems:

Rauno Aaltonen, Hans Schuller and Tony Fall:

Detail:

Aaltonen and Fall:

Tony Fall with Works team mechanics, team manager Takashi 'Waka' Wakabayashi on the left:

Thanks @HS30-H for the period photos - I especially love the driver's expressions that were captured,  even if perhaps only by happenstance.  Fall looks almost amused at the state-of-the-art rally equipment, as if he feels as if he's  been promoted to "flying-ace aviator". Aaltonen, in contrast, has a "Yeah... nah.." look of mild skepticism with the whole exercise.

A little more info to help out... You shouldn't have to spend a lot of time figuring out how the four big output transistors are connected. I can tell you that they are "push-pull" amplifiers consisting of a pair of NPN and PNP transistor pairs. In other words, each channel has a pair of complementary transistors, one NPN and one PNP.

Like this:

 

With credit to the source - https://www.electronics-tutorials.ws/amplifier/amp_6.html.  Schematically, they are connected basically like this. Note that the surrounding components like the resistors and caps are most likely a little different, but the basic scheme looks like this:

 

One other thing to note is that the four big output transistors should be electrically isolated from the aluminum plate to which they are mounted. They are bolted to the aluminum plate as a heat sink, but the connections should be mechanical only, not electrical.

With that in mind, things like bent over leads making contact to the plate would certainly prevent the unit from working, and could cause permanent damage. Can't tell from the photos if there is actually contact, but if there is, there should not be. For example:

I found these folks have a good selection of capacitors.
http://www.tubedepot.com

 

Keep it coming @Captain Obvious! FYI there was some shielding between the transistors and the other components which I removed.  I'll have to remember to re-insulate. 

I've attached a few more photos, should you be bored this afternoon at work: PCB front and back.  The back has been mirrored in order to make is possible to overlay one photo with the other, and make it easier to trace the circuit.  I'm using a simple paint program to adjust opacity - it's much easier than handling the board, and breaking wires off!  The top part of the circuit looks pretty straightforward, and not too dissimilar from your schematic.  The bottom is a bit messy, with all the extra jumper wires in the way.  There's an odd resistor in-line on the central power feed, separating the top and bottom circuits, and you are right that there are 2 large capacitors also hanging off this power feed (one on each side of the resistor).

 

Edited March 23, 20232 yr by xs10shl

20 minutes ago, 240dkw said:

I found these folks have a good selection of capacitors.
http://www.tubedepot.com

 

Thanks for the tip @240dkw - looks like a great selection of old-school electronic parts.

7 hours ago, HS30-H said:

Nissan's Works team called this system an 'Interphone' (the period English vernacular being 'Intercom') and they had already been using similar systems on previous Works rally cars. They were especially important/useful on the East African Safari Rally with its long and arduous road sections between special stages, where it was still necessary for the navigator to call the route to the driver, often at fairly high speeds (high noise). They would have been necessary on 'recce'/reconnaisance practice and ice note runs where the crew needed good communication to make accurate pace notes on events such as the Monte and RAC rallies. 

For the 1970 RAC Rally, the crews were using single-ear interphones that could be used also be used over specially-adapted Paddy Hopkirk crash helmets. Kind of unwieldy, and it is easy to see why the next step was to integrate the earphone on the inside of the helmet.

Some photos of testing in the UK prior to the 1970 RAC Rally, where the crews were getting used to the new systems:

Rauno Aaltonen, Hans Schuller and Tony Fall:

Detail:

Aaltonen and Fall:

Tony Fall with Works team mechanics, team manager Takashi 'Waka' Wakabayashi on the left:

Nice pictures Alan, thank you so much for sharing.

 I add this from a magazine, I see a red helmet on the table, is that for Aaltonen? 
Kats